In its most general form, the safety device of air-cushion type comprises a gas-inflatable airbag having an inlet opening for the entry of gas and a system for feeding the gas flow into the airbag including a gas source, a duct for communicating the inlet with the gas source, and a triggering unit that serves to detect the accident and provide a signal for generating the gas flow from the gas source to the airbag.
With the vehicle in its normal operating conditions, the airbag lies folded adjacent the driver's or passenger's seat, e.g. in the steering wheel or in the dashboard in front of passenger. During an accident, in response to signal from the sensor, the airbag must be inflated to bring it to the ready status within an average of 40 msec. In this case, the inflated airbag protects a person from shocks, vibrations etc, restricting his movements inside the vehicle.
In known safety devices, a compressed-gas reservoir or a pyrotechnical gas generator containing a solid substance which is burned to produce gas is used as the gas source in the gas flow feeding system. Combined gas sources consisting of both compressed gas and the pyrotechnical gas generator are also known in the art.
Pyrotechnical gas generators have been widely used in safety devices such as safety cushions. One disadvantage of their use, however, resides in the
Besides, the gas produced is of a toxic nature and therefore, along with operation of the safety device, a forced ventilation system needs to be actuated to remove the toxic gas the cabin.
In addition, a fresh pyrotechnical gas generator has to be installed for the repeated use of a safety device, resulting in increased maintenance costs of the safety devices.
The use of a compressed-gas reservoir to serve as the source avoids the risk of burns and poisoning.
In known safety devices of the type, however, the gas supply to the airbag is generally characterized by destroying a fragile membrane serving as the quick-exhaust valve, which, prior to starting the safety device, shuts off the flow section between the compressed-gas reservoir and the inlet opening of the airbag, (U.S. Pat. No. 5,152,550). The membrane destruction is accompanied by a production of rather sharp fragments, which, as they get into the airbag, may damage it and even cause injury to people. In order to prevent the fragments from hitting the airbag, a filter is mounted before the inlet of the airbag. The filter, however, increases the hydraulic resistance in the inlet opening of the airbag, whereby its filling rate is slowed down.
Moreover, for repeated use of such safety device, either the membrane alone or the whole gas-flow feeding system has to be replaced, which requires a special skill from the serviceman making the replacement operation, thus increasing the maintenance costs of the safety device.
This drawback may be eliminated by placing a multiuse quick-exhaust valve between the gas source and the airbag inlet, such as disclosed, for example, in RU, C1, 2005249.
The valve device of RU, C1, 2005249 comprises a body forming a valve cavity with three ducts communicating with the valve cavity: a first duct lying between the valve cavity and the low-pressure space, a second duct between the valve cavity and the high-pressure space, and a third duct connecting the valve cavity, via the control valve, with the atmosphere and the controlling pressure source.
Located within the duct is a valve seat including at least two spaced annular flanges combined to form a circular passage tapering towards the low-pressure space.
The valve comprises a stop member including a movable dome-shaped shutoff device with its vertex facing the first duct and a hollow cylindrical guide with its outer openings coaxial with the first and second ducts, respectively, both located inside the valve cavity and jointed in a telescopic manner.
The movable shutoff device is made of an elastic material and consists of a domed part and a cylindrical part.
The third duct passes through the valve body and the body of the hollow guide, connecting the guide cavity, via the control valve outside the quick-exhaust valve body, either with the atmosphere or with an external source of the controlling pressure.
In the valve ready to work (closed position), the gas pressure within the guide cavity and beneath the domed part of the shutoff device is equal to that within the high-pressure space. The dome-shaped part of the shutoff device is snug against the annular flanges of the seat, whereas between the end faces of the cylindrical part of the shutoff device and the guide, there is formed an annular gap communicating the space beneath the domed part with the valve cavity.
As the valve is operated (i.e. brought to an open position), the guide cavity and, hence, the cavity beneath the dome of the shutoff device, is relieved of gas pressure through the third duct. The consequence of the pressure relief is a drop in the pressure forcing the domed part of the shutoff device against the seat. The shutoff device then moved off the seat, moving along the guide as far as its end, so that the flow section of the first duct is opened.
It will be noted that the valve having a flow area of up to 20 cm is opened within the time not exceeding 1 msec.
In order to bring the valve to an initial, i.e. closed, position, compressed gas is supplied along the third duct to the guide cavity from an external control pressure source. The increased pressure acts upon the domed part of the shutoff device which is thus moved along the guide towards the first duct, closing it.
The use of the aforementioned quick-exhaust valve, rather than fragile membranes, in safety devices such as an inflatable safety cushion, would prevent the formation of fragments. In addition, the valve of RU, C1, 2005249 is a multiple-action device, and its use in the safety device would result in lower maintenance costs of the same.
The presence of an external control gas source, however, leads to a rather large-sizes valve, thus limiting its applications, in particular, as concerns safety devices. Furthermore, because of the external control gas source, the valve closing time substantially exceeds its opening time, which puts further limitations on the applications of such valve. Specifically, the valve device of Patent RU, C1, 2005249, being a quick-exhaust valve, fails to provide a controllable fill-up of the airbag in the safety device.
Known in the art are methods of bringing the inflatable airbag to readiness, wherein the process of filling the airbag is dependent on variable parameters such as the mass of the person protected, his position relative to location of the inflated airbag, the speed of the vehicle at the time of the accident, etc.
It is known, for example, that in order to restrict the movement of bulky and heavy driver/passenger, as the vehicle collides at a high speed, there is a need for the airbag to be rapidly filled up to a higher excess pressure, while the protection of a small person (such as a child), with a low speed at the moment of collision, requires a slower airbag inflation rate with a lower excess pressure, so as to avoid injuring the person to be protected by too rigid airbag, while providing a sufficient fillup of the airbag to allow an effective restriction of the person's displacement.
Known in the art are safety devices in which the gas source, for the control-label filling of the airbag, is made multi-element, i.e. consisting of two or more gas generators (U.S. Pat. No. 6,168,200), or two or more pressure-gas reservoirs (DE, C, 4011492,) or else including both the gas generator and the pressure-gas reservoir, i.e. combined gas sources (U.S. Pat. No. 5,738,371).
The airbag filling in said devices is controlled by providing a preset time delay between initiations of the gas flow from the gas source elements (U.S. Pat. No. 6,168,200, DE, C 4011492).
Such airbag fillup control, however, fails to provide the filling conditions required for optimum protection.
This is due to a limited range of available airbag-filling regimes defined at the device design stage and specified by initial parameters of the gas source, namely, by the number of its components and the delay between their actuation times. The specified airbag-filling mode, as it is brought to readiness, does not depend on the nature of the accident.
Besides, the devices with a multielement gas source, particularly those including several tanks with compressed gas, are rather bulky and have a more complex system of gas supply to the airbag. Specifically, in DE, C, 4011492, each reservoir is provided with a separate pipe for gas supply to the airbag.
Also known in the art is a safety device providing a wider range of airbag-filling modes available (U.S. Pat. No. 5,400,487). In this device, the multi-element gas source includes at least two pyrotechnical gas generators of different output. Moreover, the gas-flow supply triggering unit comprises a vehicle acceleration transducer, an IR sensor for measuring the position of the person to be protected with respect to the airbag, and a computer. As the computer processes the signals arriving from the sensors during the development of the accident, it determines the shape of the “amount of gas enclosed vs time” curve, which is optimum for protection of persons. According to a specific curve, the computer chooses the sequence and delay times for igniting different gas generators are selected in accordance with nine probable types of emergency situations.
In other words, in this method and embodiment, the range of available airbag-filling modes is also defined by the initial parameters of the gas source.
In addition, the airbag-filling regime, at the time of accident, is based on the information obtained and analyzed only up to the moment of igniting the last gas generator, so that the airbag-filling cannot be controlled during the accident, as would be desired to provide optimum protection.
Further the more than one gas generator will increase the size of the device. Again, the repeated use of the safety device would require the gas generators to be replaced, thereby increasing the operating costs of the device.